Where I believe it was simply +/- and you didn't lose a point for negging someone. I know there was some benefit so people would drive-by neg, and people wouldn't neg unnecessarily, but some people also deserved to be negged.
One thing that would be interesting to implement, but way too difficult, would be that the first person that negs a comment would be forced to reply. This way, you wouldn't get the people that simply say "I disagree with your opinion, I'll neg you", at least they would have to reply and discuss it. It would stop trolls from just negging everyone. But then you might also get people that reply "I disagree" and that's it. Like I said, this is way too complicated too and not realistic.